An apparatus for performing wireless communication in a wireless communication system (for example, a communication terminal or a base station) may include an envelope modulator to amplify RF signals. The envelope modulator includes a linear amplifier and a switching amplifier. The switching amplifier supplies most power for power amplification, and the linear amplifier serves to remove ripples generated in the switching amplifier. Therefore, while the switching amplifier operates in a relatively low frequency band, the linear amplifier should be able to operate in a relatively high frequency band.
In a high-efficiency switching amplifier supplying most power, once an optimal inductance for determining an operating frequency is determined, the operating frequency is fixed to one value, thereby ensuring the optimal efficiency for one target operating frequency.
With the increasing complexity of communication systems and the advent of various communication protocol standards, the envelope modulator is required to operate in one or more operating frequency bands. An envelope modulator that includes one or more operating frequency bands is called a multi-mode envelope modulator, in which the modes mean different communication modes, or different communication protocol standards. For example, the modes may include 3rd Generation Partnership Project (3GPP), Long Term Evolution (LTE), Enhanced Data rates for Global Evolution (EDGE), Code Division Multiple Access (CDMA), Wideband CDMA (WCDMA), Mobile Worldwide interoperability for Microwave Access (Mobile WiMax), and such.
When operating with multiple modes, the envelope modulator can hardly maintain its high efficiency in different modes because a bandwidth and a Peak-to-Average Power Ratio (PAPR) of an input signal are different according to the modes. In particular, compared with the linear amplifier, the switching amplifier, which supplies a substantial amount of current, operates in a low frequency and takes charge of a high-efficiency operation. In a multi-mode operation, if an input bandwidth of the envelope modulator increases, an operating frequency of the switching amplifier should also increase. In this case, if the operating frequency of the switching amplifier is optimized for the highest input frequency, the switching amplifier can no longer perform the optimal operation for the low input frequency, thus reducing the power amplification efficiency.
Designed to be optimized for only one communication mode, communication protocol standard, or operating frequency, the conventional envelope modulator may not ensure its high efficiency when operating with other modes or communication protocols in a system requiring multiple modes.